The present invention generally relates to safety restraint systems and more particularly to an improved web guide or D-ring. The typical three-point seat belt system 10 as shown in FIG. 1 comprises a retractor 22 (mounted in the seat or on a vehicle pillar), a seat belt 24, a web guide (also referred in the art as a web guide) 26 (often mounted on the B or C-pillar), a tongue 28 and a seat belt buckle 30 (mounted to a seat frame or to the floor). The web guide 26 is shown in FIG. 2. A web guide such as 26 generally includes a load-bearing plate or wire form 40 with a fastener-receiving opening 42 and a thin seat belt opening or slot 44. That portion of the plate or wire 40 below opening 44 defines a belt-receiving surface 46 upon which the seat belt slides. The seat belt 24 slides upon surface 46 as the belt protracts and retracts from and to the retractor. The friction in the seat belt system defines in part the spring constant of the rewind spring that acts on the spool of the retractor and which must generate a spring force sufficiently high to overcome friction in the system and pull or rewind a determinable extended length of seat belt (also referred to as webbing). As can be appreciated, the restoring force of the spring is proportional with the spring constant and as the spring constant increases (with increasing system friction) the inherent force applied by the shoulder belt upon the occupant""s shoulder increases. Many occupants find that a high level of belt force on the shoulder is objectionable.
In order to reduce one parameter contributing to the total system friction, the prior art has proposed to replace the static surface 46 of the web guide 26 with a roller 50 that is shown in FIG. 3. The roller is rotationally secured via, for example, an axle (or two stub axles) 52 to opposite sides 54 of the web guide about opening 44. As can be appreciated the webbing support surface previously provided by 46 is now provided by the outer diameter of the roller. One of the benefits of using a roller, as mentioned above, is the reduced friction in the system as sliding friction is replaced by rolling friction.
Reference is made to FIG. 4, which is a plan view showing the seat belt system 10 in a condition used by an occupant 60, seated upon a seat 62. As can be seen, the tongue 28 is locked within the buckle 30. In this orientation, the web guide 26 will generally rotate about its pivot point (fastener) toward the front of the vehicle. This orientation is further shown in FIG. 4a. FIG. 4 also shows the resultant force vector F acting on the webbing as it extends across the web guide 26 and is urged downwardly by the rewind force of the spring. As expected, the use of the roller 50 reduces the level of friction generated by or acting on the seat belt. Because of this reduced friction force however, in concert with the downwardly directed force F, the seat belt is encouraged to slide sideways on the roller into the rearward (downwardly) side (or end) (see numeral 64) of opening 44. Depending on the forces involved, the seat belt can become jammed between the plate 40 and the roller 50. Additionally, as the occupant pulls the tongue from its stowed position, as the tongue is inserted in the buckle the geometry of the generated forces increases the tendency of belt jamming when a bi-directional roller is used in the web guide.
The propensity for the seat belt to slide toward the end of slot 44 increases as the roller rotates, which occurs on buckling-up and may occur during other times when the belt is worn such as when the occupant moves forward and rearward. Also, as the angle of the web guide increases, it be comes easier for the webbing to get stuck (which in the art is called roping or dumping) within the spaces near the rear edge 64 about the roller. When an occupant releases the tongue from the buckle, the webbing will quickly assume the orientation as shown in FIG. 1 in which the seat belt segments on either side of the slot 44 (or roller) are generally in a parallel condition.
It is an object of the present invention to provide a seat belt web guide having an improved performance characteristic.
A further object of the present invention is to provide a web guide that utilizes a roller but one that rotates only when the webbing is retracting and one that when incorporated into a safety system makes the safety system more comfortable to use.
Accordingly the invention comprises a safety system including a web guide comprising: a frame; a roller rotationally supported in relation to the frame; and a one-way clutch for permitting the roller to rotate in a first direction and for prohibiting the roller from rotating in an opposite second direction. The roller will generally be sufficiently wide to support the width of a seat belt (webbing). The exterior surface of the roller can be flat or crowned.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.